Bi-stable permanent magnet actuation is a technique employed to move and magnetically hold the armature in electromechanical actuator devices including some valves. In bi-stable permanent magnet actuators, permanent magnets are employed in a manner that places their magnetic field in a bi-stable state to allow the secondary magnetic field produced in a control coil to divert the permanent magnet's magnetic field in one of two directions within the surrounding material.
Typically the activation circuit arrangement for bi-stable permanent magnet actuators use switches connected between the power source and the control coil to alternately direct the current from the power source in one of two directions through the control coil. One switching activation circuit arrangement that can be used with most bi-stable permanent magnet actuators to produce a bi-directional current directly from a power source is an H-bridge, like the one shown in U.S. Pat. No. 4,751,487, FIG. 7, wherein pairs of mechanical switches are simultaneously turned on to deliver the activation current to the control coil. For bi-stable permanent magnet actuators with low magnetic strength permanent magnets, like those of G.B. Pat. No. 2,297,429A and G.B. Pat. No 2,349,746A, activation circuit arrangements like U.S. Pat. No. 4,271,450, U.S. Pat. No. 4,257,081, G.B. 2,349,746A, and E.P. Pat. No. 0,380,089A2 can be used, wherein a capacitor is connected in series with the control coil (generally of a relay) and responsible for providing the reset current as a discharge current therefrom.
These activation circuit arrangements, however, require that the power source be fixed at or above the power required to achieve the desired current or activation current through the control coil. That is, in these activation circuit arrangements, the control coil is the primary power load. Whereby, the source power PS=VAIA=VA2/R becomes a function of the control coil's resistance R and the desired voltage or activation voltage VA, where IA=VA/R is the activation current. Thus, as the control coil resistance increases, to say R2, with increased number of turns to overcome high magnetic forces by increasing the amp-turns (i.e., the activation current times the number of turns or magnetic force), as would occur in prior art, the new activation voltage VA2, thus the increased power PS2=VA2/R2=VA2IA2, would need to be raised to achieve the same activation current IA=V2A2/R2=VA/R. For example, a bi-stable permanent magnet actuator having a control coil with a total resistance of R=10 ohms that requires an activation current of IA=10 Amps at VA=100 Volts would needs a continuous power source of PS=1000 Watts. Then by increasing the number of turns, where say, the resistance increases by R2=25% R, the voltage VA2=25% VA, thus power PS2=25% PS, would need to increase by 25%. This fact makes high magnetic holding force bi-stable permanent magnet actuators hard to use with energy saving power sources in today's art, like solar power, or with activation circuit arrangements like U.S. Pat. No. 4,271,450, U.S. Pat. No. 4,257,081, G.B. 2,349,746A, E.P. Pat. No. 0,380,089A2 and others in the art, as high magnetic holding force requires high amp-turns or high input power.
What is needed, therefore, is a power source to activation circuit arrangement for bi-stable permanent magnet actuators with high magnetic holding force that is more adaptable to energy saving applications.
In the art of bi-stable permanent magnet latching actuators, there are several bi-stable permanent magnet variations.
One example is the Dual Position Latching Solenoids of U.S. Pat. No. 3,022,450 and variations thereof, having a toroidal permanent magnet and two adjacent control coils that are centrally placed about a magnetic core armature with the permanent magnet radially poled perpendicular to the movement of the magnetic core and incased in a magnetic housing to place the permanent magnet's magnetic field or flux in a bi-stable state in the magnetic core and housing to allow the control coils, when activated, to produce a secondary magnetic field within the magnetic core that alternately diverts the permanent magnet's magnetic field or flux in one of two directions within the magnetic core and housing. Due to the toroidal shape of the permanent magnet, the holding force can be increased by increasing in the magnetic field strength of the permanent magnet or by thickening the permanent magnet without increasing the toroid diameter. This allows the control coil diameters to remain the same. It is understood that the magnetic holding force can also be considerably increased by slightly increasing the permanent magnet's, and thus the actuators, toroid diameter.
Another example is the G.B. pat. No 2297429A, having two linear rows of permanent magnets, one row on either side of an open ended magnetic core armature, and two adjacent control coils about the magnetic core armature with the permanent magnets linearly poled perpendicular to the movement of the magnetic core. Although similar in operation to the Dual Position Latching Solenoid as disclosed in U.S. Pat. No. 3,022,450, in G.B. pat. No 2297429A, the open ended magnetic core allows a large magnetic field or flux loss. As such, the magnetic field or flux from the permanent magnet is directed bi-stable in two directions by the control coils but stable in the loss direction at the open ends of the magnetic core. Increasing the magnetic field strength of the permanent magnets or adding more permanent magnetics lead to increase magnetic field or flux loss at the open ends of the magnetic core. It is understood that this magnetic field or flux loss would require increased magnetic field strength of the permanent magnets and increase power to the control coils over the Dual Position Latching Solenoid as disclosed in U.S. Pat. No. 3,022,450 for equal magnetic holding force.
Many bi-stable permanent magnet latching actuators used in the art today are similar to G.B. pat. No 2349746A or U.S. Pat. No. 6,057,750, having a single, centrally position permanent magnet poled parallel with the movement of a magnetic core armature, and adjacent control coil about the magnetic core armature. Although similar in operation to the Dual Position Latching Solenoid as disclosed in U.S. Pat. No. 3,022,450, in G.B. pat. No 2297429A or U.S. Pat. No. 6,057,750, the single, centrally position permanent magnet and control coil diameter are both subject to the size of the magnetic core. As such, the size and control coil of this type of actuator increases directly with the size of the permanent magnet. It is understood that for or a given permanent magnet type and field strength, the size, control coil and therefore power for this type of actuator increases faster than the Dual Position Latching Solenoid (DPLS) as disclosed in U.S. Pat. No. 3,022,450 for equal magnetic holding force.
Since the power for actuators similar to G.B. Pat. No. 2297429A and G.B. Pat. No. 2349746A increase with magnet size faster than with the DPLS actuators, DPLS actuators provide the best option to use with energy saving power sources at greater magnetic holding forces. However, in the art of bi-stable permanent magnet actuators, the DPLS actuator has not been adopted for use. This fact may actually be due to its higher magnetic holding capability, which limits its size to the low power systems in today's art. What is needed, therefore, is a power source to activation circuit arrangement for bi-stable permanent magnet actuators like DPLS actuators that will make them more applicable for use in today's art of energy savings.